1. Field of the Invention
The present invention relates generally to methods and systems for image processing, and more particularly to methods and systems for de-screening digitally scanned documents.
2. Description of Related Art
Almost all printed matter, except silver-halide photography, is printed using halftone screens. The need to estimate the halftone frequency and magnitude stems from the fact that almost all printed matter, with the exception of a few devices like dye-sublimation or silver-halide photography, is printed out using halftone screens. These halftones are very specific to the printing device and when scanned and re-halftoned may cause visible artifacts and/or unacceptable Moiré patterns if not properly removed. The suppression of halftones is especially important for color documents, since these are typically printed with four or more color separations containing slightly different screens at different angles and or frequencies, and these may interact with each other to cause undesirable spatial artifacts.
The successful removal of the original halftone screens is based on the ability to accurately estimate the local frequency. Therefore there is a need for an improved method and apparatus for estimating the halftone screen frequency and magnitude.